Estimation of airborne rat-derived antigens by ELISA

Comparison of methods to assess airborne rat and mouse allergen levels. I. Analysis of air samples

Airborne laboratory-animal allergens can be measured by several methods, but little is known about the effects of important differences in methodology. Therefore, methods used in research projects in The Netherlands, the UK, and Sweden were compared. Seventy-four sets of three parallel inhalable dust samples were taken by a single operator in animal facilities in the three countries, and analyzed in parallel by the three institutes for rat and mouse urinary allergen. Rat-allergen levels measured by RAST inhibition (UK) were 3000 and 1700 times higher than levels measured by enzyme immunoassay (EIA)-sandwich methods with polyclonal rabbit (The Netherlands) or monoclonal mouse (Sweden) antibodies, while the difference between the two EIA-sandwich methods was much smaller: a factor of 2.2. For mouse allergen, an inhibition radioimmunoassay (RIA) with rabbit antimouse antibodies (UK) gave 4.6 and 5.9 times higher concentrations than sandwich EIAs with rabbit polyclonal antibodies (Sweden and The Netherlands), while the difference between the two sandwich EIAs was, on average, 1.6-fold. Thus, although levels of rat and mouse aeroallergens are significantly correlated, the assay type gives large differences in absolute concentrations, and interlaboratory technical differences affect even the same assay type. Conversion factors can aid comparison between studies, and, in the long term, assay standardization is desirable.

Comparison of methods to assess airborne rat and mouse allergen levels. II. Factors influencing antigen detection

Potential factors influencing antigen detection in immunoassays for measuring rat or mouse aeroallergen (i.e., assay setup, antigen specificities, standard extracts used, and antigen decay) were investigated in a three-country study (the UK, The Netherlands, Sweden). An inhibition enzyme immunoassay (EIA) setup gave nominal rat urinary allergen (RUA) sample values seven times higher than a sandwich EIA setup utilizing identical antibodies and standards. In immunoblotting experiments, pooled patient serum and polyclonal rabbit antibodies partly detected different rat antigens; monoclonal antibody specificity could not be determined. Immunoblot detection of mouse urinary antigens (MUA) by the polyclonal rabbit antibodies from all laboratories was similar. In both the RUA and the MUA assays, urinary antigen standards were detected with similar potency, except purified Rat n 1, which was an inefficient inhibitor in the RUA RAST inhibition. In the sandwich EIA RUA assays, a rat room-dust extract was detected with 700800-fold less sensitivity than rat urine, whereas in the RAST RUA assay, dust inhibited equally with rat urine. Simulated decay did not decrease the potency of urinary antigen in any assay. Thus, assay setup and choice of detection antibodies strongly influence the nominal allergen levels. We recommend the use of standardized and characterized antibodies and standard extracts in sandwich EIAs to measure airborne rodent urinary allergens.

Measurement of airborne rat urinary allergen in an epidemiological study

The suitability of radioallergosorbent test (RAST) inhibition to quantify occupational exposure to rat urinary aeroallergen (RUA) has been assessed. When using a constant pool of rat allergic sera, the reproducibility of the assay over 1 year was comparable to that reported for other immunoassays; at 50% RAST inhibition the inter-assay coefficient of variation (CV) was 7.0% and the intra-assay CV was 3.0%. The assay was highly specific for rat urine; mouse urine was 1100-fold less potent at inhibiting the rat urine RAST system. Significant inter-assay variation in the 'high' control was not due to batch variation and was relatively small when compared with the variation in RUA concentrations in the occupational environment. Measurement of workplace RUA exposure demonstrated that those directly involved in the care of rats experienced the highest RUA exposure of the nine occupational groups studied (animal technicians GM = 23.10 micrograms/m3), dead animals (e.g. post mortem GM = 1.60 micrograms/m3, scientists GM = 0.67 microgram/m3) and rat tissue (e.g. slide production GM = 0.04 microgram/m3). In view of the complexity of rat allergens, RAST inhibition is an appropriate method for the quantification of occupational exposure to rats.

The relationship between exposure to rats and antibody production in man: IgG antibody levels to rat urinary protein

An ELISA procedure has been developed to measure specific IgG antibodies against rat urine. Using this method antibody levels in individuals with differing exposure levels to rat have been measured. Mean antibody titres in groups of workers regularly exposed to rats were higher than those in groups currently or totally non-exposed. However, only in the group of workers exposed and sensitized to rats were IgG levels significantly elevated. Despite this significant difference in mean antibody titres there was considerable overlap between individuals in each group, and there was no direct relationship between exposure to rats and levels of IgG anti-rat urine antibody. Our results suggest a stronger correlation between sensitization to rats and the levels of antigen-specific IgG antibodies.

Level of airborne bovine epithelial antigen in Finnish cowsheds

Samples of airborne particulate material were collected from 18 Finnish cowsheds both at stationary sites and in breathing zones. The concentrations of bovine epithelial antigen (BEA) in samples were analyzed by the immunochemical enzyme-linked immunosorbent assay (ELISA) inhibition test. For total dust and BEA measurements the range of results among cowsheds was wide. In the breathing zone the mean concentration of total dust was 2.4 +/- 1.5 mg/m3 and of BEA 460 +/- 300 ng/m3. The concentrations of total dust and BEA were significantly lower at stationary sites than in breathing zones. Correlation analyses of total dust and BEA concentrations revealed that only moderate correlations existed, and they were not statistically significant (P greater than 0.05). Correlations between BEA concentrations in feeding passage or manure passage and breathing zone were at most only moderate (rs 0.29, P = 0.12 and rs 0.42, P = 0.02, respectively). The correlation of BEA concentrations between the two stationary sites was relatively strong and significant (rs 0.71, P = 0.004), suggesting that the variation in BEA concentrations between cowsheds is real. The effects of brushing and number of animals on total dust and BEA concentrations were studied statistically in samples from the breathing zone. No high or significant correlations were observed.

ELISA method for measurement of airborne levels of major laboratory animal allergens

Three types of air-sampling apparatus (the Air-Sentinel, Burkard Personal Sampler and Casella Personal Sampler) were compared for their use in sampling the air in situations where individuals are exposed to laboratory animals, and a cascade impactor was used to determine the sizes of particles carrying the allergens under investigation. An ELISA, using monospecific antisera raised to selected major allergens of the mouse, rat and rabbit, i.e. mouse Ag 1 (mouse urinary prealbumin), rat Ag 4 (rat urinary prealbumin) and rabbit Ag R1, was developed to assay the extracts obtained from the samplers. This ELISA system was able to detect greater than 5 ng/m3 of allergen in sampled air. The rat and mouse allergens were shown to be carried mainly on particles of 6-18 micron, whereas the rabbit allergen was also found on particles of 2 micron and smaller. Allergen levels correlated well with the number of animals present in the room and the degree of activity during sampling. A protective filtered-air hood, when worn during surgical operation procedures, was shown to reduce effectively the level of rat allergen breathed by an individual.